In a mobile communications system such as the GSM cellular system call processing, control and management require many messages to be passed within the system. Mobility introduces a relatively random element in the amount of work that an office such as the Mobile services Switching Centre (MSC) within the system must perform because of the unpredictable nature of the location of mobile stations.
Normally engineering guidelines can be used to limit overload conditions (for example by limited provisioning of trunks and signalling support such as Signalling system No.7 links). Even with such limits, the amount of work that can be offered to an office can be beyond the capacity of the equipment because offices are provisioned for sustained levels of service and typically not to accommodate unusual or periodic spikes.
In an office serving mobile stations, office engineering can have severe limitation because of the transient nature of the subscribers and because of the disassociation between the subscriber equipment and the office equipment. As a result some form of control must be put in place to maintain the maximum amount of processing (i.e.: processing that results in service provision to the mobile customer or processing which provides revenue generation to the service provider) with the minimum amount of disruption.
The GSM specifications require that switching elements should exchange messages indicating overload and also recommend some ways in which traffic towards an overloaded switch may be reduced, such as by call gapping.
It is an object of the present invention to provide an overload control mechanism to allow a mobile switch to function at its optimum condition when the traffic load is beyond its capacity.